How to check if a deque is empty

Question

Is try-catch the only method to do that?

Answer 1

If d is your deque, use

if d:     # not empty else:     # empty 

This will implicitly convert d to a bool, which yields True if the deque contains any items and False if it is empty.

Answer 2

There are two main ways:

1. Containers can be used as booleans (with False indicating the container is empty):

2. Containers in Python also have a __len__() method to indicate their size.

Here are a few patterns:

non_empty = bool(d)     # Coerce to a boolean value  empty = not d           # Invert the boolean value  if d:                   # Test the boolean value     print('non-empty')  while d:                # Loop until empty     x = d.pop()     process(x)  if len(d) == 0:         # Test the size directly    print('empty') 

The latter technique isn't as fast or succinct as the others, but it does have the virtue of being explicit for readers who may not know about the boolean value of containers.

Other ways are possible. For example, indexing with d[0] raises an IndexError for an empty sequence. I've seen this used a few times.